1. Field of the Invention
The present invention relates to a technology for recording information onto an information recording medium such as an optical disc.
2. Related Art
In recent years, attention has been paid to an optical disc such as a DVD-RAM as a large capacity information recording medium, and the optical disc has been developed and merchandised for an external memory of a computer and for picture and voice recording. In general, the optical disc is provided with a spiral or concentric track on a disc surface and laser beams are irradiated along the track, thereby recording and reproducing information. Moreover, the track is further divided into a plurality of sectors which become the minimum unit for recording and reproducing information data.
As a method for recording information onto the optical disc, there has generally been known a light modulation recording method for modulating the intensity of a laser beam irradiated on the track onto which data are to be recorded according to the data to be recorded. Typically, there have been known recording methods applicable to an optical disc material over a wide range, for example, a phase change type optical disc, an organic pigment type optical disc, a magneto-optical disc and the like.
Moreover, a pulse width modulation method (which will be hereinafter referred to as a “PWM method”) has been known as a method for recording data onto an optical disc at a high density. The PWM method serves to perform modulation such that the edges of front and rear edges of a recording mark correspond to “1” of a digital signal, and can assign more bits into the recording mark having the same length as compared with a pulse position modulation method for performing modulation such that the position of the recording mark corresponds to “1” of the digital signal. Therefore, the PWM method is suitable for an enhancement in the density.
In the PWM method, the width of the recording mark has information. Therefore, it is necessary to homogeneously form the recording mark on the front and rear edges without distortion. However, in the case where a long mark is to be particularly recorded by the heat regenerating effects of a recording film by means of the phase change type optical disc or the like, the width of the recording mark in the radial direction is gradually increased toward a latter half portion. In other words, there has been a problem in that the recording mark is distorted like a teardrop. In order to solve the problem, there has been proposed a recording method for forming one recording mark by the irradiation of a plurality of short pulse chain (which has been disclosed Japanese Patent Laid-Open Publication No. 3-185628, for example).
Moreover, there has also been proposed a method for changing and recording pulse positions corresponding to a recording leading edge portion and a recording mark terminating portion in a recording pulse chain are changed and recorded for each mark length/space length of data to be recorded, thereby compensating for a peak shift by a thermal interference between marks and a frequency characteristic obtained during reproduction (which has been disclosed in Japanese Patent Laid-Open Publication No. 7-129959, for example).
The operation for forming the recording mark of good quality by changing the position of the recording pulse as described above is generally referred to as “recording compensation”.
In the case where the position of the recording pulse is to be changed for the recording compensation, it is necessary to change the edge position of the recording pulse in a time unit which is much shorter than one channel bit of the record data. Therefore, it is hard to generate the recording pulse by a synchronous circuit using a clock signal having a one-channel bit cycle. Therefore, there has generally been taken such a structure that the position of the recording pulse is changed by signal delay means capable of controlling a delay amount (which has been disclosed in the Japanese Patent Laid-Open Publication No. 7-129959, for example).
In the signal delay means, however, the delay amount is generally changed readily for a change in a source voltage, a temperature or the like. In the case where the change in the delay amount which is obtained by a fluctuation in the source voltage, a fluctuation in the temperature or the like is comparatively small, the quality of the record data is not affected. However, in the case where the change in the delay amount is comparatively great, the position of the recording pulse is shifted from a proper position. Therefore, the recording mark cannot be formed correctly so that recording and reproducing characteristics are deteriorated.
In a conventional optical disc recording device, a delay amount for a specific mark length/space length has been fixedly set and there has no means for correcting the positional shift of the recording pulse which is caused by a fluctuation in a source voltage, a temperature or the like.
The conventional optical disc recording device has had such a structure that separate signal delay means is provided for each pulse portion to individually perform control when a plurality of pulse portions in the recording pulse are to be changed in different delay amounts. For this reason, separate signal delay means are required corresponding to the number of the pulse portions to be changed independently. Consequently, a circuit scale tends to be increased. Furthermore, as the position variable range of the pulse portion is more increased, a delay length to be required for individual signal delay means is more increased so that the circuit scale is more enlarged.